Biodegradable polymers such as polymers from glycosides, poly(lactic acid), polyvinyl alcohol, polycaprolactone, have a broad range of industrial and biomedical applications as films. However, articles made from these materials or the films often suffer deficiencies such as brittleness, poor impact strength, poor tear strength, poor clarity, water sensitivity, poor processability, etc. In many instances selected deficiencies can be improved by preparing blends of biopolymers with other biopolymers or synthetic polymers. A problem associated with blending biopolymers is compatibility with other polymers, especially less polar polymers. Orientation with strain assisted crystallization of amorphous polymers may be used to increase the stiffness or modulus of films as well as elongation. Such orientation process decreases the elongation-at-break in the direction of the lower orientation.
Also, utilization of starch polymers is attractive due to the renewable nature and the compostability, which eases burdens on landfills, but articles fabricated from starch are very brittle, and this poor impact toughness limits commercial applications of pure starch articles. Starch can be blended with a variety of polymers to improve the properties of starch, but as the starch content increases the tensile strength and elongation at break both decrease. See, Bikiaris (D. Bikiaris and C. Panayiotou, Journal of Applied Polymer Science, 1998, vol 70, p. 1503). Anhydrous plasticized starch blended with polyethylene has been compatibilized with maleic anhydride-grafted polyethylene (Bikiaris). See also, WO2006042364. Maleic anhydride-grafted polyethylene has also been used in starch alloys containing 20 to 80% starch (e.g., U.S. Pat. No. 5,635,550) and in a blend of destructurized starch (e.g., U.S. Pat. No. 5,409,973).
It would also be desirable to produce articles from resin compositions with >80% starch content thereby improving the biodegradability of the resulting resin composition. These articles are more difficult to toughen because they comprise a higher proportion of the brittle starch and could also have the brittle starch as the continuous or co-continuous phase. For example, use of hydroxypropyl-modified, high-amylose starch in combination with less than 10% polyvinyl alcohol has been described (WO 00/36006). However, these articles have inferior impact properties, particularly at <40% relative humidity.
Accordingly, it is desirable to develop a modified composition, and its blends, with improved processability and physical properties and to articles made from the composition or from a multilayer structure comprising the composition.